Conventionally, before a fuel cell is put into normal operation, there has been carried out a method in which the current with higher current density than the predetermined current density is passed to raise an output of the fuel cell, namely—pre-running. The effect of raising unit voltage can be obviously achieved when pure oxygen gas for working as an oxidant is supplied to a cathode, and when pre-running is carried out with the current density as much as possible, and the duration as long as possible.
However, the above-mentioned pre-running method is operationally complicated and time-consuming. Besides, as the heavy current running is needed, it causes flooding and massive heat, both of which may damage an electrolyte membrane. The so-called flooding refers to the phenomenon of the blockage of the cathode flow way by the water generated on the cathode. Due to the existence of such an unfavorable factor, the use of the above-mentioned method can hardly obtain an inherent capacity of the fuel cell itself effectively.
Patent Literature No. 1 discloses the activation technique of water electrolysis. This technique pays attention to the fact that in a fuel cell having an ion exchange membrane formed by a polymer electrolyte membrane, and a unit cell including an anode and a cathode for sandwiching the ion exchange membrane, and separators, the fuel cell is activated by increasing water content of the ion exchange membrane. In this technique, while the humidified gas is supplied to the cell, 1.3 v or more of electrolytic voltage is applied to the cell for water electrolysis. According to Patent Literature No. 1, water in an electrolyte membrane is compulsively decomposed into hydrogen and oxygen by the electrolysis, and in accordance with this, the concentration gradient of water molecules in the electrolyte membrane increases, and due to this, the water diffusion speed in the electrolyte membrane increases. As a result, water in the humidified gas flows to the electrolyte membrane to rapidly increase the water content.
Patent Literature No. 2 discloses the technique of restoring the degradation of a fuel cell. This technique pays attention to the fact that when metal ions such as iron, nickel, and the like are trapped into a high polymer electrolyte membrane, the ionic conductivity of the high polymer electrolyte membrane decreases and the power generation performance is weakened. In this technique, when a fuel cell is degraded, a fluid for restoring degradation which contains a reductant for restoring degradation (hydrazine or hydrazine salt) with stronger reducing power than that of hydrogen is brought into contact with the high polymer electrolyte membrane, so as to restore the degradation of the power generation performance of the fuel cell, whose degradation is caused by the metal ions adhered to the high polymer electrolyte membrane. According to Patent Literature No. 2, the metal ions such as iron, nickel and the like, which are trapped into the high polymer electrolyte membrane, which are reduced by the reductant for restoring degradation with stronger reducing power, and which is precipitated as metals. Thus, the metal ions are removed, and the power generation performance is enhanced.
In addition, Patent Literature No. 3 discloses the technique of activating a high polymer electrolyte membrane fuel cell, in which modules of the high polymer electrolyte membrane of a fuel cell is boiled in deionized water or mild acid water (such as hydrogen peroxide water). Besides, Patent Literature No. 3 discloses the technique of activating a high polymer electrolyte membrane fuel cell, in which alcohol is supplied to a gas supply way of the high polymer electrolyte membrane fuel cell to adapt an electrode diffusion layer to alcohol. Patent Literature No. 3 also discloses the technique of activating a high polymer electrolyte membrane fuel cell, in which the power generation of modules of the high polymer electrolyte membrane fuel cell is carried out with oxygen utilization rate of 50% or more, and the average cell voltage is kept to be 0.3 v or less.
(Patent Literature No. 1: Japanese Unexamined Patent Publication (KOKAI) No. 6-196, 187)
(Patent Literature No. 2: Japanese Unexamined Patent Publication (KOKAI) No. 2000-260,453)
(Patent Literature No. 3: Japanese Unexamined Patent Publication (KOKAI) No. 2000-3718)
However, according to the above-mentioned patent literatures 1-3, procedures are complicated, and time-consuming, and besides, flooding and massive heat caused by the heavy current running, may damage the electrolyte membrane. Since these defects exist, in the above-mentioned method, it is not necessarily clear that an inherent capacity of the fuel cell itself is obtained.
The present invention is made, taking account of the above-mentioned circumstances. An object of the present invention is to provide an activation method of a polymer electrolyte fuel cell which is advantageous to activation and raises cell voltage.